Basic Mechanical Engineering

Basic mechanical engineering This site will help you to know the Basics of mechanical engineering concepts and terms. We have tried our level best to make the definitions and explanations as simple as possible and in the futuer many things will be include....

Wednesday, March 18, 2009

Tips to Pass Mechanical Aptitude Test

If you are looking for a technical position or career path, your educational and professional certificates will not be enough for you to achieve this target. This is because there is overwhelming evidence that a the majority of public and corporate organisations are now employing Mechanical Aptitude Tests to short-list their applicants. This type of job aptitude tests assesses your depth in the realms of physical and mechanical theories. They vary from the conventional reasoning tests where you don't need any specialist knowledge. But for the Mechanical aptitude tests you will need to be well versed in the subjects of mechanical and technical knowledge.

When you are going to take a Mechanical Aptitude Test you will be presented with a variety of questions regarding various mechanical devices like pulleys, levers, tools, springs, gear and several other accessories. You must ensure that your knowledge in elementary sciences is refreshed and up-to-date. One area where mechanical reasoning tests are mandatory is Military jobs and emergency services. In these cases, you can expect questions focusing more on the theoretical aspects rather than calculations. In contrast technical and craft related positions will require you to solve calculations.

Some of the Mechanical Aptitude Tests can include questions specific to a particular industry. For instance, a test conducted by a fire service organisation may contain queries regarding fire fighting instruments.

Companies have found great benefit is using a variety of Psychometric Tests. Firstly, it helps the organisation reduce the large number of applicants they have received for a limited number of posts, to a manageable number of potential candidates. In these cases, an aptitude test helps the company to eliminate the unsuitable or unfit applicants quickly and efficiently. Secondly, additional aptitude tests and exercises can be used to further reduce candidates during the interview stage down to a shortlist.

Before preparing for a mechanical reasoning test, you need to know how you can best enhance your chances of cracking them and raising your score to above the average. There are some categories of aptitude tests that you may have to face. These include IQ tests, numerical and logical ability tests, verbal reasoning tests, personality tests and so on.

For cracking a mechanical reasoning test, you need to practice in a systematic and rigorous way. Online aptitude tests help one to overcome this problem. One of the best websites for offering you the opportunity to try these employment aptitude tests is www.psychometric-success.com. As the proverb goes - practice makes perfect - and these Aptitude Tests are no exceptions.

You will find that most of these tests are arranged in a multiple choice format and they are meant to be completed within a stipulated period of time. Sometimes it may not be possible for you to finish them, but practice will help you get farther than other applicants. Generally, the reasoning tests do not have a fixed pass mark, but you need to aim for a high score to stand out. Keeping these things in mind, you need to prepare for the mechanical reasoning tests to be successful. If you want to find out more about mechanical aptitude tests visit www.psychometric-success.com. This site will provide you detailed information about mechanical and other psychometric tests.

Wednesday, December 17, 2008

Thermodynamic Systems and Processes Summary• A thermodynamic system is a collection of matter and space with its boundariesdefined in such a way that the energy transfer across the boundaries can be bestunderstood.• Surroundings are everything not in the system being studied.• Systems are classified into one of three groups:Isolated system - neither mass nor energy can cross theboundariesClosed system - only energy can cross the boundariesOpen system - both mass and energy can cross theboundaries• A control volume is a fixed region of space that is studied as a thermodynamicsystem.• Steady state refers to a condition where the properties at any given point within thesystem are constant over time. Neither mass nor energy are accumulating within thesystem.• A thermodynamic process is the succession of states that a system passes through.Processes can be described by any of the following terms:Cyclic process - a series of processes that results in the systemreturning to its original stateReversible process - a process that can be reversed resulting in no changein the system or surroundingsIrreversible process - a process that, if reversed, would result in a change tothe system or surroundingsAdiabatic process - a process in which there is no heat transfer across thesystem boundariesIsentropic process - a process in which the entropy of the system remainsunchangedPolytropic process - the plot of Log P vs. Log V is a straight line, PVn =constantThrottling process - a process in which enthalpy is constant h1 = h2, work= 0, and which is adiabatic, Q=0.

Monday, November 3, 2008

Wednesday, October 29, 2008

The field of thermodynamics deals with systems that are able to transfer thermal energy into at least one other form of energy (mechanical, electrical, etc.) or into work. The laws of thermodynamics were developed over the years as some of the most fundamental rules which are followed when a thermodynamic system goes through some sort of energy change.What is Thermodynamics?:Thermodynamics is the field of physics that deals with the relationship between heat and other properties (such as pressure, density, temperature, etc.) in a substance. Specifically, thermodynamics focuses largely on how a heat transfer is related to various energy changes within a physical system undergoing a thermodynamic process. Such processes usually result in work being done by the system and are guided by the laws of thermodynamics.Laws of ThermodynamicsHeat transfer is guided by some basic principles which have become known as the laws of thermodynamics, which define how heat transfer relates to work done by a system and place some limitations on what it is possible for a system to achieve.

The heat capacity, C, of an object is the ratio of change in heat (energy change - denoted by delta-Q) to change in temperature (delta-T).C = delta-Q / delta-T

The heat capacity of a substance indicates the ease with which a substance heats up. A good thermal conductor would have a low heat capacity, indicating that a small amount of energy causes a large temperature change. A good thermal insulator would have a large heat capacity, indicating that much energy transfer is needed for a temperature change.Ideal Gas Equations:

There are various ideal gas equations which relate temperature (T1), pressure (P1), and volume (V1). These values after a thermodynamic change is indicated by (T2), (P2), and (V2). For a given amount of a substance, n (measured in moles), the following relationships hold:Boyle's Law (T is constant):P1V1 = P2V2Charles/Gay-Lussac Law (P is constant):V1/T1 = V2/T2Ideal Gas Law:P1V1/T1 = P2V2/T2 = nRR is the ideal gas constant, R = 8.3145 J/mol*K. For a given amount of matter, therefore, nR is constant, which gives the Ideal Gas Law.Laws of Thermodynamics:Zeroeth Law of Thermodynamics - Two systems each in thermal equilibrium with a third system are in thermal equilibrium to each other.First Law of Thermodynamics - The change in the energy of a system is the amount of energy added to the system minus the energy spent doing work.Second Law of Thermodynamics - It is impossible for a process to have as its sole result the transfer of heat from a cooler body to a hotter one.Third Law of Thermodynamics - It is impossible to reduce any system to absolute zero in a finite series of operations. This means that a perfectly efficient heat engine cannot be created.The Second Law & Entropy:

The Second Law of Thermodynamics can be restated to talk about entropy, which is a quantitative measurement of the disorder in a system. The change in heat divided by the absolute temperature is the entropy change of the process. Defined this way, the Second Law can be restated as:In any closed system, the entropy of the system will either remain constant or increase.

By "closed system" it means that every part of the process is included when calculating the entropy of the system.

1.Define stress and strain. Write down the S.I. and M.K.S. unitsof stress and strain.2. Explain clearly the different types of stresses and strains.3. Define the terms: Elasticity, elasticlimit, Young'smodulusandModulus of rigidity.4. State Hooke's law.5. Three sections of a bar are having different lengths and differentDiameters. The bar is subjected to an axial load p. Determine the total changein length of the bar. Take Young's'modul of different sections same.6. Distinguish between the following, giving due explanation: (1) Stress and strain, (2) Force and stress, and (3) Tensile stress and compressive stress.7. Prove that the total extension of a uniformly tapering rod ofDiameters D1 and D2, whenthe rod issubjectedto an axial load P is given by 4PL dL .CededWhere L=Total length of the rod8. Define a composite bar. How will you find the stresses and load Carried by each member of a composite bar?9, Define modular ratio, thermal stresses, thermal strains and Poisson’s ratio.10. A rod whose ends are fixed to rigid supports, is heated so thatRise in temperature is rc. Prove that the thermal strain and stressesSetup in the rod are given by, Thermal strain=a. T and Thermal stress=a.T.E.Where a=Co-efficient of linear expansion.11. What is the procedure of finding thermal stresses in a composite Bar?12 what do you mean by 'a bar of uniform strength’?13 Find an expression for the total elongation of a bar due to its Own weight, when the bar is fixed at its upper end and hanging freely at the lower end.14 Find an expression for the total elongation of a uniformlyTapering rectangular bar when it is subjected to an axial load P.15.Define and explain the following terms:Shear force, bending moment, shear force diagram and bendingMoment diagram.16.What are the different types of beams? Differentiate betweena cantilever and a simply supported beam.17.What are the different types of loads acting on a beam?18.Differentiate between a point load and a uniformly distributed load.19.What are the. Sign conventions for shear force and bendingMoment in general? '20.Draw the S.F. and, B.M. diagrams for a cantilever of length LCarrying a point load W at the free end.21.Draw the S.F. and B.M. diagrams for a cantilever of length LCarrying uniformly distributed load of w per m length over its entire length.22.Draw the S.F. and, B.M. diagrams for a cantilever of length LCarrying a gradually varying load from zero at the free end to w per unitLength at the fixed end.23.Draw the S.F. and B.M. diagrams for a simply supported beamof length L carrying a point loads Wat its middle point.24.Draw the S.F. and B.M. diagrams for a simply supported beamCarrying a uniformly distributed load of w per unit length over the entireSpan. Also calculate the maximum B.M.25.Draw the S.F. and B.M. diagrams for a simply supported beamCarrying a uniformly varying load from zero at each end to w per unit lengthat the centre. '26.What do you mean by point of contra flexure? Is the point ofContra flexure and point of inflexion different?27. How many points of contra flexure you will have for simplySupported beam overhanging at one end only?28.How will you draw the S.F. and B.M. diagrams for a beam?29.Which is subjected to inclined loads?30.What do you mean by thrust diagram?31.Draw the S.F. and B.M.diagramsfor a simply supported beam of length L which is subjected to a clockwise couple 11at the centre of the Beam.32.Define the terms: bending stress in a beam. neutral axis andsection modulus.33.What do you mean by 'simple bending' or 'pure bending’?34.What are the assumptions made in the theory of simple bending?35.Derive an expression for bending stress at a layer in a beam.36.What do you understand by neutral axis and ", moment ofResistance?37.Prove the relation,M=L=~I y R'l=M.O.I.where M=Bending moment,y=Distance from N.A.f=Bending stress,R=Radius of curvature.E=Young's modulus, and(Bangalore University, Jan. 1990)38.What do you mean by section modulus? Find an expressionfor section modulus for a rectangular, circular and hollow circular sections.39.How would you find the bending stress in unsymmetricalsection?40.What is the meaning of 'Strength of a section’?41.Define and explain the terms: modular ratio, fletched beamsand equivalent section.42.What is the procedure of finding bending stresses in case offletched beams when it is of (i) a symmetrical section and (ii) anunsymmetrical section?43.Explain the terms: Neutral axis, section modulus, and momentof resistance. (Bangalore University, July 1988)44.Show that for a beam subjected to pure bending, neutral axiscoincides with the centroid of the cross-section.(Bangalore University, March 1989)45.Prove that the bending stress in any fiber is proportional to the distanceof that fiber from neutrally in beam. (BhavnagarUniversity, 1992)46.Define the terms: Torsion, torsion rigidity and polar momentof inertia.47.Derive an expression for the shear stress produced in a circularshaft which is subject to torsion. What are the assumptions made in thederivation?48.Find an expression for the torque transmitted by a hollowCircular shaft of external diameter=Do and internal diameter=Dj.49.Define the term 'Polar modulus'. Find the expressions for polarModulus for a solid shaft and for a hollow shaft50.What do you mean by 'strength of a shaft' 151.Define torsional rigidity of a shaft. Prove that the torsionalrigidity is the torque required to produce a twist of one radian in a unitlength of the shaft.52.Find an expression for strain energy stored in a body which dueto torsion or Prove that the strain energy stored in a body due to torsion is givenBy, 2 U=.Lxv. 4Cwhere q=Shear stress on the surface of the shaft,C=Modulus of rigidity, andV=Volume of the body.53.A hollow shaft of external diameter D and internal diameter dis subjected to torsion, prove that the strain energy stored is given by,2U=~ (D2+cf) xV4CDwhere V=Volume of the hollow shaft andq=Shear stress on the surface of the shaft.54.What is a spring? Name the two important types of spring.